Horizontal linearity correction coil

Abstract: A horizontal linearity correction coil is used for a television receiver having a cathode ray tube of a wide deflection angle and has excellent productivity, quality and loading respectively. The ferrite magnetic core has the flanges (16, 17 and 18) at both ends and the middle and has a hollow shape at one winding core portion (19) of the ferrite magnetic core. The windings (22 and 23) are wound around the winding core portions (19 and 20) and the permanent magnets (24 and 25) are combined to both end flanges (16 and 18).

Description: BACKGROUND OF THE INVENTION FIELD OF THE INVENTION The present invention relates to a horizontal linearity correction coil to be used for a television receiver or the like. DESCRIPTION OF THE RELATED ART In a television receiver using a cathode ray tube which has a wide deflection angle of 112 degrees and which has a plane fluorescent screen called a flat face, when a lattice-shaped cross hatch pattern 1 is displayed on the screen as shown in Fig. 4, a distortion occurs to widen the distance in the horizontal direction of the screen as shown by 1a and 1b at portions between the center and the left end portion and between the center and the right end portion of the screen. As shown in Fig. 5, a horizontal deflection current 2a is linear with respect to time t (that is, this current shows a constant change rate with the change of time), and cathode rays (electron beams) of a cathode ray tube 3 shown in Fig. 6 are electromagnetically deflected at a constant angle (  a1 =  a2 =  a3 =  a4 ). Since the fluorescent screen of the cathode ray tube 3 is plane, the displayed positional dimensions of the fluorescent screen of the cathode ray tube 3 become l a1 ≠ l a2 ≠ l a3 ≠ l a4 . In order to correct this distortion, first and second linearity correction coils 6 and 7 are connected in series to a horizontal deflection coil 5 which is connected to a horizontal deflection output circuit 4 and a capacitor 8 is connected to this second horizontal linearity correction coil 7 so as to form a horizontal deflection circuit as the circuit is shown in Fig. 7. Fig. 8 shows the electrical characteristics of the first and second horizontal linearity correction coils 6 and 7. The characteristic of the first horizontal linearity correction coil 6 is designated by L 6 and the characteristic of the second horizontal linearity correction coil 7 is designated by L 7 . The characteristic L 6 of the first horizontal linearity correction coil 6 shows a peak value of inductance in the middle between "0" of a horizontal deflection current I H and a maximum value at the minus side. The characteristic L 7 of the second horizontal linearity correction coil 7 shows a peak value of inductance in the middle between "0" of the horizontal deflection current I H and a maximum value at the plus side. Thus, the peak value of the characteristic L 6 is larger than the peak value of the characteristic L 7 . In order to obtain a characteristic designated by L 8 , by combining the characteristic L 6 and the characteristic L 7 , the first and second horizontal linearity correction coils 6 and 7 are connected in series, and the horizontal deflection current 2a is corrected as shown by 2b as shown in Fig. 5 so that the change rate of the horizontal deflection current with respect to time is changed. Particularly, the change rates of the horizontal deflection current become smaller at the positions of the intermediate portions between the center portion and the left end portion and between the center portion and the right end portion of the fluorescent screen of the cathode ray tube. The electromagnetic deflection angles with respect to the time change of the cathode rays (electron beams) of the cathode ray tube 3 become  b1 ≠  b2 ≠  b3 ≠  b4 . However, the positional dimensions displayed on the fluorescent screen of the cathode ray tube 3 become l b1 = l b2 = l b3 = l b4 , so that the distortion is corrected as shown in Fig. 9. Consequently, when the lattice-shaped cross hatch pattern 1 is displayed on the screen, a constant distance can be maintained as shown in Fig. 10. The first and second horizontal linearity correction coils 6 and 7 have the structures as shown in Fig. 11 and Fig. 12, respectively. That is, the first horizontal linearity correction coil 6 comprises a first ferrite magnetic core 9 of drum type, a first winding 11 wound around the first ferrite magnetic core 9 and a first ferrite magnet 13 combined at one of flanges 9a of the first ferrite magnetic core 9. Similarly, the second horizontal linearity correction coil 7 comprises a second ferrite magnetic core 10 of drum type, a second winding 12 wound around the second ferrite magnetic core 9 and a second ferrite magnet 13 combined at one of flanges 10a of the second ferrite magnetic core 9. The first horizontal linearity correction coil 6 shown in Fig. 11 is structured to form the first ferrite magnetic core 9 with the diameter of a first winding core portion 9b at the rate of 0.33 to 0.35 of the diameter of the first flange 9a. The second horizontal linearity correction coil 7 shown in Fig. 12 is structured to form the second ferrite magnetic core 10 with the diameter of a second winding core portion 10b at the rate of not larger than 0.3 of the diameter of the second flange 10a so that a magnetic saturation is generated in small inductance. SUMMARY OF THE INVENTION As described above, according to the conventional horizontal linearity correction coil, the two horizontal linearity correction coils 6 and 7 are connected in series to obtain the combined characteristic. Therefore, it is necessary to make small the variations of the respective characteristics of the horizontal linearity correction coils 6 and 7 and to optimize the pairing of the two, so that substantial manpower is required for production management and inspection of the characteristics, with extreme disadvantages in production costs. It is an object of the present invention to provide a highly productive and high-quality horizontal linearity correction coil that eliminates the above-described conventional drawbacks. According to the precharacterizing clause of claim 1, the present invention starts from a teaching as is known from US-PS-3,806,853. Said document describes an apparatus for compensation of pin cushion distortion of the picture displayed by a TV-set. For the compensation of asymmetrical top and bottom pin cushion distortions, said prior art document provides for a casing being provided with one or more openings and at least one magnet in said opening to influence the magnetic field of the saturable reactor type transformer. GB-A-2,157,087 describes a linearity coil with two magnets at the ends thereof, said magnets having a hollow donut shape. This linearity coil is meant for compensating for linearity distortions. According to the invention, the above object is achieved by a horizontal linearity correction coil comprising: A horizontal linearity correction coil comprising: a ferrite magnetic core having a first flange at one end portion of said ferrite magnetic core, a second flange at an intermediate portion of said ferrite magnetic core, a third flange at the other end portion of said ferrite magnetic core, a first winding core portion for combining said first flange and said second flange, and a second winding core portion for combining said second flange and said third flange; first and second windings wound around said first and second winding core portions of said ferrite magnetic core, respectively; first and second permanent magnets magnetized in an axial direction of said ferrite magnetic core, combined respectively to said first and second flanges of said ferrite magnetic core; a first horizontal linearity correction coil portion comprising said first winding and said first permanent magnet; and a second horizontal linearity correction coil portion comprising said second winding and said second permanent magnet; said first horizontal linearity correction coil portion generating a magnetic saturation in small inductance; characterized in that there is a hollow portion formed in said first flange; the number of turns of said first winding is smaller than the number of turns of said second winding; and a magnetic force of said first permanent magnet is smaller than a magnetic force of said second permanent magnet. Preferably, the first winding and the second winding are connected in series and so that magnetic fluxes are generated in different directions by said first and second windings. Said first and second windings may be wound continuously and in different directions. Preferably, a peak value of inductance versus horizontal deflection current characteristic of said second winding is at least two times of a peak value of inductance versus horizontal deflection current characteristic of said first winding. According to a further preferred embodiment, the first permanent magnet combined to said first flange has a hollow donut shape. With the above-described structure, the horizontal linearity correction coil formed by the hollow-shaped winding core portion generates a magnetic saturation in inductance smaller than the inductance at the horizontal linearity correction coil portion that is structured by the non-hollow shaped winding core portion, thereby to correct a distortion in the horizontal deflection of the cathode ray tube of which fluorescent screen is plane. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a cross sectional diagram for showing one embodiment of the horizontal linearity correction coil according to the present invention. Fig. 2 is an equivalent circuit of the same. Fig. 3 is a characteristic diagram of the same. Fig. 4 is an explanatory diagram for explaining an image distortion of the cathode ray tube having a general wide deflection angle. Fig. 5 is a characteristic diagram of a horizontal deflection current when two conventional horizontal linearity correction coils are used. Fig. 6 is an explanatory diagram for showing an electromagnetic deflection of the cathode rays of the cathode ray tube having the general wide deflection angle. Fig. 7 is a circuit diagram for showing the conventional horizontal deflection circuit. Fig. 8 is an electrical characteristic diagram of the two conventional horizontal linearity correction coils. Fig. 9 is an explanatory diagram for showing an electromagnetic deflection of cathode rays of the cathode ray tube having a wide deflection angle when the two conventional horizonal linearity correction coils are used. Fig. 10 is an explanatory diagram for showing the image state of the cathode ray tube. Fig. 11 is a cross sectional diagram for showing one of the conventional horizontal linearity correction coils. Fig. 12 is a cross sectional diagram for showing the other conventional horizontal linearity correction coil. DESCRIPTION OF THE PREFERRED EMBODIMENT One embodiment of the horizontal linearity correction coil according to the present invention will be explained below with reference to the drawings. Fig. 1 is a cross sectional diagram for showing one embodiment of the horizontal linearity correction coil according to the present invention, Fig. 2 is an equivalent circuit thereof, and Fig. 3 shows a characteristic diagram thereof. In the drawings, 15 designates a ferrite magnetic core, and the ferrite magnetic core 15 has an upper end flange 16, an intermediate flange 17, a lower end flange 18, a first winding core portions 19 for combining the upper end flange 16 and the intermediate flange 17, and a second winding core portion 20 for combining the intermediate flange 17 and the lower end flange 18. A hollow portion 21 is formed in the upper end flange 16 and the first winding core portion 19. First and second windings 22 and 23 are wound around the winding core portions 19 and 20, respectively. The windings 22 and 23 are connected so that magnetic fluxes generated by the windings 22 and 23 are mutually in the different directions when the windings 22 and 23 are connected in series. The windings 22 and 23 are connected so that they are wound in the different directions when they are wound continuously. First and second permanent magnets 24 and 25 made of a ferrite magnet or the like magnetized in the axial direction of the ferrite magnetic core 15 are combined to the end surfaces of the outsides of the upper end flange 16 and the lower end flange 18 of the ferrite magnetic core 15, respectively. The two permanent magnets 24 and 25 have different intensities of magnetic forces. The first permanent magnet 24 to be combined to the upper end flange 16 is a hollow-shaped donut type. This shape is made to open the space of the hollow portion 21 so that heat is not enclosed in this hollow portion 21. As described above, as the ferrite magnetic core 15, the hollow portion 21 is provided in the first winding core portion 19 for combining the upper end flange 16 and the intermediate flange 17. A first horizontal linearity correction coil portion 26 comprises the first winding 22 wound around the first winding core portion 19 and the first permanent magnet 24 combined at the upper end flange 16. The second horizontal linearity correction coil portion 27 comprises the intermediate flange 17, the lower end flange 18, the second winding core portion 20, the second winding 23, and the second permanent magnet 25. Thus, the first horizontal linearity correction coil portion 26 that utilizes the first winding core portion 19 where the hollow portion 21 is formed can generate a magnetic saturation in small inductance. The hollow portion 21 is formed to have a thickness of about a half of the thickness of the intermediate flange 17 and the diameter of the hollow portion 21 is determined based on the diameter of the first winding core portion 19 by taking into account the magnetic saturation. A detailed example of the horizontal linearity correction coil according to the present invention will be explained. The ferrite magnetic core 15 is fabricated so that the diameters of the upper end flange 16, the intermediate flange 17 and the lower end flange 18 are set to be 15 mm respectively, the diameters of the first and second winding core portions 19 and 20 are set to be 5 mm respectively, the diameter of the hollow portion 21 is set to be 3 mm, the thicknesses of the upper end flange 16, the intermediate flange 17 and the lower end flange 18 are set to be 2.2 mm respectively, the winding widths of the first and second winding core portions 19 and 20 are set to be 8.6 mm respectively, the whole length of the ferrite magnetic core 15 is set to be 23.8 mm, and the material of the ferrite magnetic core 15 is Ni-Zn soft ferrite. A twisted set of about six copper lines, each line having a diameter of 0.22 mm, insulation coated with a polyurethane resin, is wound around the first and second winding core portions 19 and 20 around the ferrite magnetic core 15, to form the first and second windings 22 and 23. The reason for using the set twisted lines for the first and second windings 22 and 23 is to prevent the cupper lines from heating due to the current flowing through them whose resistance components at high frequency, for example, at a horizontal deflection frequency 15.73 KHz of the television receiver increase because of the skin effect generated on the cupper lines. The set twisted lines are wound by 71 turns around the second winding core portion 20 of the ferrite magnetic core 15 and the set twisted lines are wound by 42 turns around the first winding core portion 19 having the hollow portion 21, thereby to structure the second and first windings 23 and 22. As the first and second permanent magnets 24 and 25 to be combined on both ends of the ferrite magnetic core 15, an isotropic dry molding barium hard ferrite is used, with diameters 15 mm for the first and second permanent magnets respectively, the thickness of 6.5 mm for the second permanent magnet 25, and the thickness of 2.5 mm for the first permanent magnet 24, and a hollow portion of a diameter 8 mm is formed at the center of the first permanent magnet 24. The equivalent circuit of the horizontal linearity correction coil having the above-described structure is as shown in Fig. 2 and the inductance versus current characteristic is as shown in Fig. 3. As a result, a combined characteristic similar to the one as explained for the prior-art example shown in Fig. 8 is obtained, and the lattice-shaped cross hatch pattern of the screen can take equal distances as shown in Fig. 10. In this case, it is assumed that a peak value of the inductance of the second horizontal linearity correction coil portion 27 is at least two times of a peak value of the inductance of the first horizontal linearity correction coil portion 26. The reasons why the peak value of the inductance of the second horizontal linearity correction coil portion 27 is set at least two times of the peak value of the inductance of the first horizontal linearity correction coil portion 26 will be explained. The value of inductance of the horizontal linearity correction coil that is required for correcting a distortion of a horizontal deflection current caused by the horizontal deflection coil and the resistance component of the horizontal deflection circuit is about 15 percent of the value of inductance of the horizontal deflection coil at the portion of the maximum value at the minus side of the horizontal deflection current. It is assumed that this value is "L1". When the horizontal deflection current is linearly changed with respect to time t as the horizontal deflection current 2a shown in Fig. 5, the extension of the distance in the horizontal direction, which occurs in the cross hatch pattern on the screen at portions between the center and the left end portion and between the center and the right end portion, is about 1.5 times as described in the prior art in the cathode ray tube which has the wide deflection angle of 112 degrees and which has the plane fluorescent screen called a flat face. The value of the inductance of the horizontal linearity correction coil which is required for correcting this distortion is about 1.5 times of "L1", which is described above, in the middle between "0" of the horizontal deflection current and the maximum value at the minus side. Further, the value of the inductance of the horizontal linearity correction coil in the middle between "0" of the horizontal deflection current and the maximum value at the plus side is about 50 percent of "L1". Because the inductance component which is increased for correcting the distortion is required. Concretely, when the value of the inductance of the horizontal deflection coil is for example 1300 µH, the value of "L1" is defined as following. L1 = 1300 × 0.15 = 195 [µH] In the cathode ray tube which has the size of 73,66 cm (29 inches) and has the wide deflection angle of 112 degrees and which has the plane fluorescent screen called a flat face, the deflection center of the electron beam is inside of the fluorescent screen by about 240 mm. When the electron beam is electromagnetically deflected at the conformal velocity, the distance l 0 in the horizontal direction of the fluorescent screen which the range from the deflection angle 0° to 33° is divided equally among three is defined as following. l 0 = (240 × tan33°) / 3 ≒ 52 [mm] Further, the distance l d in the horizontal direction of the fluorescent screen from the deflection angle 33° to 44° is defined as following. l d = 240 × (tan44° - tan33°) ≒ 76 [mm] The ratio l d /l 0 of the distance l d to the distance l 0 is defined as following. l d /l 0 = 76 / 52 ≒ 1.46 Consequently, the value L left of inductance of the second horizontal linearity correction coil portion 27 in the middle between "0" of the horizontal deflection current and the maximum value at the minus side is defined as following. L left = L1 × l d /l 0 = 195 × 1.46 ≒ 285 [µH] Further, the value L right of inductance of the first horizontal linearity correction coil portion 26 in the middle between "0" of the horizontal deflection current and the maximum value at the plus side is defined as following. L right = (L1 × l d /l 0 ) - L1 = (195 × 1.46) - 195 ≒ 89.7 [µH] Thus, the peak value of the inductance of the second horizontal linearity correction coil portion 27 is set at least two times of the peak value of the inductance of the first horizontal linearity correction coil portion 26. Referring to Fig. 3, "A" designates a characteristic of the first horizontal linearity correction coil portion 26 when the hollow portion 21 of the diameter 3 mm is formed in the first winding core portion 19, "B" designates a characteristic of the second horizontal linearity correction coil portion 27, and "C" designates a combined characteristic of both of the horizontal linearity correction coil portions 26 and 27. "D" shows a characteristic of the first horizontal linearity correction coil portion 26 when the hollow portion 21 is not formed in the first winding core portion 19, "E" shows a characteristic of the first horizontal linearity correction coil portion 26 when the hollowing portion 21 of a diameter 2 mm is formed in the first winding core portion 19, and "F" shows a characteristic of the first horizontal linearity correction coil portion 26 when the hollow portion 21 of a diameter 2.5 mm is formed in the first winding core portion 19. As described above, by changing the diameter of the hollow portion 21 of the first winding core portion 19, the inductance versus horizontal deflection current characteristic of the first horizontal linearity correction coil portion 26 can be controlled so that the horizontal linearity correction coil according to the design of the television receiver can be provided. As is clear from the above embodiment, the horizontal linearity correction coil according to the present invention can be achieved by using one horizontal linearity correction coil in stead of two independent horizontal linearity correction coils of different characteristics that are used conventionally, with an effect that productivity can be improved significantly and desired characteristics can be satisfied completely. Further, the horizontal linearity correction coil according to the present invention uses a small number of structural parts, requires a simple loading and can reduce a loading area, which results in a large contribution to the industry.

Claims: A horizontal linearity correction coil comprising: a ferrite magnetic core (15) having a first flange (16) at one end portion of said ferrite magnetic core, a second flange (17) at an intermediate portion of said ferrite magnetic core, a third flange (18) at the other end portion of said ferrite magnetic core, a first winding core portion (19) for combining said first flange and said second flange, and a second winding core portion (20) for combining said second flange and said third flange; first and second windings (22, 23) wound around said first and second winding core portions of said ferrite magnetic core, respectively; first and second permanent magnets (24, 25) magnetized in an axial direction of said ferrite magnetic core, combined respectively to said first and second flanges of said ferrite magnetic core; a first horizontal linearity correction coil portion (26) comprising said first winding and said first permanent magnet; and a second horizontal linearity correction coil portion (27) comprising said second winding and said second permanent magnet; said first horizontal linearity correction coil portion generating a magnetic saturation in small inductance; characterized in that there is a hollow portion (21) formed in said first flange (16); the number of turns of said first winding (22) is smaller than the number of turns of said second winding (23); and a magnetic force of said first permanent magnet (24) is smaller than a magnetic force of said second permanent magnet (25). The horizontal linearity correction coil according to claim 1, wherein said first winding (22) and said second winding (23) are connected in series and so that magnetic fluxes are generated in different directions by said first and said second windings. The horizontal linearity correction coil according to claim 1 or 2, wherein said first winding (22) and said second winding (23) are wound continuously and in different directions. The horizontal linearity correction coil according to any preceding claim, wherein a peak value of inductance versus horizontal deflection current characteristic of said second winding (23) is at least two times of a peak value of inductance versus horizontal deflection current characteristic of said first winding (22). The horizontal linearity correction coil according to any preceding claim, wherein said first permanent magnet (24) combined to said first flange (16) has a hollow donut shape.

Inventors: ITO TAKANOBU, KONNO ISAGO, TSUTSUMI YUTAKA, ITO, TAKANOBU, KONNO, ISAGO, TSUTSUMI, YUTAKA
Applicants: MATSUSHITA ELECTRIC IND CO LTD, MATSUSHITA ELECTRIC INDUSTRIAL CO., LTD.
Application year: 1994
Main classification: H01F38
IPC codes: H01F38, H04N3